Elizabeth Bell, who has died aged 71 of cancer of the oesophagus, was an accomplished and versatile actor who was associated in particular with Alan Ayckbourn, although she also appeared with the English Stage Company at the Royal Court, the National theatre and at other London venues such as the Almeida and the Bush. She appeared in the inaugural season of Britain's first dedicated theatre-in-the-round, at Stoke-on-Trent, the brainchild of Stephen Joseph, whose acolytes, Peter Cheeseman and Ayckbourn, were, respectively, director and actor with the company.

Ayckbourn was already writing plays while acting at the Library theatre in Scarborough between 1957 and 1962, and that company went with him to Stoke. Bell played a secretary to Ayckbourn's leading role in Christmas V Mastermind (1962), the last of his plays in which he also acted. The other two leading women in the company were Caroline Smith (later a director) and Heather Stoney (later Ayckbourn's second wife).

Bell was struck for life by the passion and commitment to new work of these repertory theatre idealists – Joseph resembling a socialist realist poster in his paint-stained overalls, with his hammer at the ready – and she first saw Ayckbourn in the 1958 season at Scarborough, "causing a few hearts to flutter," she told his biographer, Paul Allen.

She was the daughter of Elizabeth and Neil Bell, born in Clifton, Leeds. Her father left when she was four and her mother, brother and grandmother moved to Scarborough, where she attended the girls' high school. She then opted for drama school, winning both the gold medal and the Sybil Thorndike prize at the Central School of Speech and Drama in London in 1961.

A founder member of the Victoria theatre, now the New Vic, in Newcastle-under-Lyme, Staffordshire, she went on to work at the Royal Court in Peter Gill's definitive productions of Thomas Otway's The Soldier's Fortune in 1967 and DH Lawrence's The Daughter-in-Law (on tour), and as a highly regarded, languorously beautiful Yelena in the Paul Scofield Uncle Vanya, directed by Anthony Page in 1970.

By 1971 she was living with the architect Henry Osborne who, following a divorce settlement, was converting a house he had built in Hampstead, north London, into two separate dwellings. He asked Bell if she knew of anyone who would like to buy the front half – and that is how Ayckbourn and Stoney became London neighbours of their Scarborough colleague.

Bell made numerous television appearances, notably as Thea Elvsted in John Osborne's version of Hedda Gabler in 1981, with Diana Rigg and Alan Dobie, and many radio programmes, where she was always in demand for drama as well as readings on the BBC's Woman's Hour, Front Row, Poetry Please and Night Waves.

She was also a notable member of Ayckbourn's 1987 company at the National Theatre, appearing opposite Michael Gambon in Arthur Miller's A View from the Bridge – her Beatrice was kind, anxious, perceptive, a masterclass in how to make goodness interesting; and as Anita, a dissatisfied housewife who has substituted whips, manacles and endless lovers for a pig of a husband with a Porsche and a little boat, in Ayckbourn's masterful study of a nation on the skids, A Small Family Business.

Back at Scarborough, she created the role of Imogen (played in London by Joanna Lumley) in Ayckbourn's two-part epic The Revenger's Comedies (1989) and stayed on to play Emilia in the Michael Gambon Othello (Ken Stott was Iago, Claire Skinner Desdemona) the following year, and Lizzie, an erotic and self-deceiving former showgirl who, said the Guardian's Michael Billington, talks about her career as though she had been in the Bolshoi, in a revival of Ayckbourn's brilliantly structured Taking Steps.

The better the company, the more Bell would shine, as was evident in David Hare's version of Brecht's The Life of Galileo (directed by Jonathan Kent), cast to the nines with Richard Griffiths in the lead, at the Almeida in 1994, and in Rodney Ackland's Absolute Hell (directed by Anthony Page) at the National in 1995, in which she played a socialist rich bitch in a bohemian gallery (Betty Marsden, Peter Woodthorpe, Sheila Burrell, June Brown, Barbara Hicks), supervised by Judi Dench as the hostess with the leastest.

In her later years, Bell was a mentor for Central School students, an external examiner for Trinity College London and an in-house audio describer for the National theatre. She was one of the first actors to join the InterAct reading service for hospitals and stroke clubs.

Her last stage appearances included a fussy old cleaning woman in Simon Bent's Chekhovian slice of west London low-life, Goldhawk Road, at the Bush in 1996, a powerful Duchess of York opposite Eddie Marsan's psychotic Richard III at the Pleasance in 1997, and a Rosa Kleb-like corrupt finance minister in The UN Inspector (Michael Sheen starring as the updated Gogol hero) at the National in 2005, wielding a deadly handbag containing a poisonous syringe.

In 2007 she succeeded Frances de la Tour as Miss Lintott in Alan Bennett's The History Boys in the West End, treating her, said Billington, as "a fount of practical wisdom" and leading him to conclude that the history teacher was, in fact, Bennett's real hero.

She is survived by Osborne, whom she married last year, and her stepchildren, Abigail and Ben.

Alan Ayckbourn writes: I worked with Liz in various capacities, as a director, a writer-director and in the early days as a fellow actor. So over the years I got to know her very well. We first met in our Scarborough theatre's original home in the public library when she, a tall, attractive drama student, was introduced to me, a fully fledged acting/assistant stage manager with all of 18 months' professional experience under my belt.

I remember, in the face of my cocky, faux-blasé manner, her shyness, reducing her to deep-toned monosyllables. A year or two later, considerably less shy and more vocal, she was back with the company as an actor, many of the qualities later to distinguish her as a performer already in place. A remarkable, distinctive voice, deep enough to make a 20-year-old clench his toes with excitement; in appearance, striking rather than conventionally beautiful but, onstage, blessed with that natural god-given sexual attractiveness which no amount of acting artifice or cosmetic cunning can ever quite achieve. Her range, too, in one so young, was considerable.

Having seen her perform the Strange Lady in Shaw's Man of Destiny, I promptly cast her as a 60-something dotty old spinster in A Thief in Time (needs must when budgets are limited). Later, we appeared together onstage playing eccentric lovers, Fred and Maisie, in William Norfolk's new play, The Birds and the Well Wishers, and brother and sister, Roderick and Madeleine, in David Campton's adaptation of Edgar Allan Poe's The Fall of the House of Usher.

To act with, she was a joy. To direct, she was often challenging, forever questioning, not content to accept things purely on face value and, like any good actor, never settling for anything less than dramatic truth. If that makes her sound a tough proposition, then once her questions were answered, doubts reassured, she was fiercely loyal to you and the production.

Later on, in the 1980s, I was invited by Peter Hall to form my own company at the NT. I approached Liz to ask her if she would like to be part of it, playing Beatrice opposite Gambon in A View from the Bridge and, again by stark contrast, the sexually provocative Anita in my own premiere, A Small Family Business.

Over the phone, to my surprise, she sounded hesitant, almost reluctant. It was only after I spelt it out to her that the penny dropped. She was convinced that I had phoned to offer her the understudy roles. It was another side to her which, though present in most performers, one rarely saw: uncertainty, lack of confidence and vulnerability. She was a touchingly complex, infuriatingly intriguing actor – and a fierce, loyal, dear friend.